Page 116 - Textbook of Pathology, 6th Edition

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SECTION I

Figure 5.5 Mechanisms involved in the pathogenesis of cardiac oedema.

Pulmonary Oedema Normally the plasma oncotic pressure is adequate to prevent
the escape of fluid into the interstitial space and hence lungs
Acute pulmonary oedema is the most important form of local are normally free of oedema. Pulmonary oedema can result
General Pathology and Basic Techniques
oedema as it causes serious functional impairment but has from either the elevation of pulmonary hydrostatic pressure
special features. It differs from oedema elsewhere in that the or the increased capillary permeability (Fig. 5.6).
fluid accumulation is not only in the tissue space but also in
the pulmonary alveoli. 1. Elevation in pulmonary hydrostatic pressure (Haemo-
dynamic oedema). In heart failure, there is increase in the
ETIOPATHOGENESIS. The hydrostatic pressure in the pressure in pulmonary veins which is transmitted to
pulmonary capillaries is much lower (average 10 mmHg). pulmonary capillaries. This results in imbalance between

Figure 5.6 Mechanisms involved in the pathogenesis of pulmonary oedema. A, Normal fluid exchange at the alveolocapillary membrane
(capillary endothelium and alveolar epithelium). B, Pulmonary oedema via elevated pulmonary hydrostatic pressure. C, Pulmonary oedema via
increased vascular permeability.